1. Field of the Invention
The Kolbel-Engelhardt synthesis is a well-known process for producing liquid and gaseous hydrocarbons, including hydrocarbon fuels. (See Brennstoff Chemie., Vol. 33 (1952) PA 13-21). In the process, mixtures of carbon monoxide and steam are usually contacted with an iron-based catalyst producing a broad range of linear and branched olefins and paraffins of C.sub.5 -C.sub.20 carbon number. A particularly valuable portion of the produced hydrocarbons, produced under conditions of excess hydrogen, is the C.sub.6 -C.sub.13 fraction, containing linear and branched paraffins, which is useful for internal combustion engines.
In this area, it is a general goal to improve the selectivity of the process in producing aromatic hydrocarbons for use in the chemical industry, and in particular, to improve the aromatic content of the C.sub.6 -C.sub.13 hydrocarbon fraction, especially with respect to C.sub.6 -C.sub.9 aromatic hydrocarbons in order to improve the octane number. It is known that use of C.sub.6 -C.sub.9 aromatic hydrocarbons improves the octane number and is environmentally advantageous since it obviates the need for supplementary refining runs, as now practiced, to produce current nonleaded motor gasoline.
French Pat. No. 635,950 (1927) discloses a number of Fischer-Tropsch catalysts containing copper, silver, gold, zinc or Group VIII metals, or combinations thereof, for carrying out the conversion of mixtures of CO and H.sub.2 to hydrocarbons. Also described is the use of cadmium or thallium, as equivalent promoters, in combination with the Group VIII metals, including cobalt and iron, for reducing soot formation. However, no specific mention is made of the use of thallium in particularly promoting the selectivity of an iron catalyst in the Kolbel-Engelhardt process toward the production of C.sub.6 -C.sub.11 liquid aromatic hydrocarbons, substantially containing C.sub.6 -C.sub.9 aromatics.
There is a continuing search for new and more efficient iron-based catalysts, which are inexpensive and convenient to prepare, for carrying out the Kolbel-Engelhardt process. Particularly, what is desired are iron-based catalysts which, under mild process conditions, exhibit greater selectivity to the formation of C.sub.6 -C.sub.13 liquid hydrocarbons, and particularly, C.sub.6 -C.sub.13 aromatic hydrocarbons containing a significant weight percentage of C.sub.6 -C.sub.9 aromatic hydrocarbons.